This pathway is the first that purposely does not continue to intermediary metabolism. Dibenzothiophene (DBT) is a model compound for organic sulfur in fossil fuels, and its desulfurization pathway removes this sulfur (Gray et al., 1996). The EAWAG-BBD has a separate DBT degradation pathway, but in the words of Dr. Kevin Gray (personal communication, 1996):
"We know that in this species of Rhodococcus the pathway does not continue; i.e., it stops at 2-hydroxybiphenyl (HBP) and the HBP is released into the medium. The sulfur product is incorporated into cellular biomass via sulfur assimilation pathways. That actually is the beauty of this system as far as desulfurization of fossil fuels is concerned: we do not decrease the carbon content (the 'fuel value') of our substrate molecule. If all we wanted to do was degrade the dibenzothiophene (DBT) to carbon (and energy) we would have chosen an easier and more efficient enzyme system like the biphenyl or naphthalene degradation pathways (which will mineralize DBT). However we don't want to 'degrade' DBT just 'transform' it into another molecule that can then go back into the fuel while at the same time removing the sulfur. The physiological role of this enzyme system is to obtain sulfur for growth; in fact, Rhodococcus sp. IGTS8 can use dibenzothiophene as a sole source of sulfur."The following is a text-format dibenzothiophene desulfurization pathway map. An organism which can initiate the pathway is given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This is the first pathway to have its map also available in graphic (12k) format.
Dibenzothiophene Rhodococcus sp. IGTS8 | | | dibenzothiophene | monooxygenase | | v Dibenzothiophene-5-oxide | | | dibenzothiophene | monooxygenase | | v Dibenzothiophene-5,5-dioxide | | | dibenzothiophene-5,5-dioxide | monooxygenase | | v 2'-Hydroxybiphenyl-2-sulfinate | | | 2'-Hydroxybiphenyl- | 2-sulfinate sulfinolyase | | v 2-Hydroxybiphenyl | | | v to the Biphenyl Pathway
Page Author(s): Kevin Gray
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